Patent GB-1002267-A (GB)
Title: Improvements in and relating to electric signal-translating devices, and the manufacture thereof
IPC: H01L27/00
Filed: 1962-11-29
Abstract: 1,002,267. Semi-conductor devices. PHILCO CORPORATION. Nov. 29, 1962 [Nov. 29, 1961], No. 45140/62. Heading H1K. A solid state signal translating device comprises a barrier means (i.e. a non-conducting region in a semi-conductor or insulator) with a source (emitter) contact and a control (base) contact on one side of the barrier and a collector contact on the other, the source and control being closely spaced so that tunnelling current can be provided in the adjacent region of the barrier, which flows to the collector subject to control by the source-control voltage; the arrangements may provide an amplifier with power gain. Fig. 1 shows a single crystal N-type, 1 ohm cm. germanium wafer 10 with a nickel ohmic contact 12 on one side and aluminium film (1000 A) rectifying contacts 14 and 16 on the other side separated from each other by a thin (20 A) aluminium oxide layer 18. Connections to these contacts may be provided by silver paste, pressure contacts, evaporated gold, welding or thermo compressions. Collector 12 is housed about 3V. positive and emitter contact 16 about 1 volt negative with respect to base contact 14 so that both contacts 14 and 16 are reverse biased and their depletion layers overlap under oxide layer 18 to form one continuous depletion region. An input signal 40 applied between base 14 and emitter 16 results in an amplified signal appearing across load 36 in the collector circuit. It is explained that an intense field exists in the region immediately underlying the oxide separating layer 18 which depends on the base-emitter voltage and is sufficient to provide tunnel current or, if the thickness of the spacer is made a little greater (e.g. 100 A), avalanche current, and the bulk of this current flows to the collector to provide an amplifying effect. Common base or common collector circuits may be employed and emitter and base may be interchanged. In an alternative arrangement (Fig. 4), employing an insulator as the barrier layer instead of the semi-conductor, an indium-tinoxide collector layer 52 is provided on a glass substrate 50 and covered with a polycrystalline layer (1-2Á) 54 of cadmium sulphide; this layer is evaporated on and then baked at 500 C. for 15 minutes. Aluminium contacts 58 and 60 and separating aluminium oxide layer 61 are then provided as in Fig. 1. The device operates in a manner similar to Fig. 1 provided the energy gap of the barrier material (ie. 24 e.v. for cadmium sulphide) is substantially less than that of the spacer material (7. 1 e.v. for aluminium oxide). In other embodiments the emitter and base contacts are modified to provide a long emitter-base edge for a given area by having one of the contacts comb-shaped or perforated with circular holes. Reference is made also to the lower contact layer being extremely thin (100 A) so that it is porous and thin enough to be penetrated by tunnel current as described in Specification 990,037. The semi-conductor material may be resistivity graded from emitter to collector and may consist of silicon, intermetallic compounds, intrinsic, polycrystalline, large or narrow band gap material; for high temperature use oxides, sulphides and halides of metals or organic insulators may be used. The collector contact can be partly rectifying and if an insulator is used the emitter and base contacts need not consist of metal specially selected to provide a barrier layer. The device may be encapsulated in a nitrogen atmosphere.